1. Field of the Invention
The present invention relates to storable water-microsphere suspensions for use in well cements and methods of cementing wells.
2. Description of the Prior Art
Hydraulic cement compositions are commonly utilized in subterranean well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby strings of pipes such as casings and liners are cemented in well bores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of the well bore and the exterior surfaces of a pipe string disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe string in the well bore and bonds the exterior surfaces of the pipe to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented.
In some locations, the subterranean zones or formations into or through which wells are drilled have high permeabilities and low compressive and tensile strengths. As a result, the resistances of the zones or formations to shear are low and they have very low fracture gradients. When a well fluid such as a hydraulic cement composition is introduced into a well bore penetrating such a subterranean zone or formation, the hydrostatic pressure exerted on the walls of the well bore can exceed the fracture gradient of the zone or formation and cause fractures to be formed in the zone or formation into which the cement composition is lost. While lightweight cement compositions have been developed and used which contain microspheres for reducing the density of the cement compositions, the microspheres are usually dry blended with the cement utilized followed by mixing the dry blend with water. This procedure, however, is troublesome because it is difficult to obtain a constant cement-microsphere blend due to the differences in density between the cement and microspheres. While the microspheres can be added to the mix water, because the microspheres are lighter than the water, they float in the water.
Thus, there are needs for storable water-microsphere suspensions for use in preparing lightweight well cement compositions which can be stored at the well site or on an offshore platform for use when needed.
The present invention provides storable water-microsphere suspensions for use in well cementing compositions and methods of cementing well bores which meet the needs described above and overcome the deficiencies of the prior art. In one aspect of the present invention, storable water-microsphere suspensions for use in forming lightweight well cement compositions are provided. While being stored, the water-microsphere suspensions do not separate for at least three weeks and do not require stirring or agitation before use. The storable water-microsphere suspensions are basically comprised of water, microspheres and an effective amount of a suspending agent selected from the group consisting of microfine, i.e., sub-micron particle size or colloidal materials and gel forming polymers. The microspheres utilized in the suspensions can be fly ash microspheres, glass microspheres or recycled glass microspheres.
In another aspect of the present invention, improved methods of cementing well bores with lightweight cement compositions are provided. The methods are comprised of the following steps. A water-microsphere suspension for reducing the density of a well cement composition is stored comprised of water, microspheres and an effective amount of a suspending agent selected from the group consisting of microfine or colloidal materials and gel forming polymers. The water-microsphere suspension is combined with a cement composition comprised of a hydraulic cement and water. The cement composition including the water-microsphere suspension is introduced into the well bore, and thereafter the cement composition is allowed to set.
The objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.